Short range radar small in size and low in power consumption and controlling method thereof

ABSTRACT

A transmitter section radiates a short range wave to a space. A receiver section has a detector circuit composed of a branch circuit which receives a reflection wave of the short range wave radiated to the space by means of the transmitter section and branches in phase a signal of the reflection wave into first and second signals, a linear multiplier which linearly multiplies the first and second signals branched in phase by means of the branch circuit, and a low pass filter which samples a baseband component from an output signal from the linear multiplier. A signal processor section carries out an analyzing process of an object which exists in the space based on an output from the receiver section. A control section makes a predetermined control with respect to at least one of the transmitter section and the receiver section based on an analysis result from the signal processor section.

This application is a U.S. National Phase Application under 35 USC 371of International Application PCT/JP2005/018661 filed Oct. 7, 2005.

TECHNICAL FIELD

The present invention relates to short range radars and a method forcontrolling thereof. In particular, the present invention relates toshort range radars and a method for controlling thereof employing atechnique for achieving, with a simple and small sized construction,short range radars used in the range of a quasi millimeter band (UWB:Ultra-wideband) from 22 GHz to 29 GHz allocated for automotive radars orradars for walk assistance of visually handicapped persons, inparticular, and achieving low power consumption, from among short rangeradars for radiating pulse waves of narrow width (short range waves) toa space in a predetermined cycle, receiving and detecting a reflectionwave from an object which exists in the space, and analyzing the objectwhich exists in the space based on its detected output.

BACKGROUND ART

A pulse radar for investigating an object in space by usingconventionally known pulse waves basically has a construction as shownin FIG. 14.

That is, in this pulse radar 10 shown in FIG. 14, upon the receipt of atrigger signal G outputted in a predetermined cycle Tg from a controlsection 16 described later, a transmitter section 11 generates a pulsewave Pt having a predetermined width and a predetermined carrierfrequency synchronized with the trigger signal G and radiates thegenerated pulse wave to a space via a transmitter antenna 11 a.

This pulse wave Pt is reflected by means of an object 1 a which existsin a space 1, and its reflection wave Pr is received by a receiverantenna 12 a of a receiver section 12, and then, the received wave isdetected by means of a detector circuit 13.

A signal processor section 15 analyzes the object 1 a which exists inthe space 1 based on a timing with which a detected output D isoutputted from the receiver section 12 while a timing with which a pulsewave is transmitted from the transmitter section 11 is defined as areference timing, for example, or its outputted waveform.

The control section 16 makes a variety of controls with respect to thetransmitter section 11 and the receiver section 12 based on a processingresult or the like of the signal processor section 15.

A basic construction of such pulse radars 10 is disclosed in patentdocuments 1 and 2 below.

Patent document 1: Jpn. Pat. Appln. KOKAI Publication No. 7-012921

Patent document 2: Jpn. Pat. Appln. KOKAI Publication No. 8-313619

From among the pulse radars having such a basic construction, thefollowing two types of pulse radars are devised as automotive radarswhich have been practically available in recent years.

The development of pulse radars of a first type is underway for thepurpose of assistance at the time of high speed running such asprevention of collision of automobiles or running control byinvestigating a narrow angle range with high output and in long distanceusing a millimeter wave band (77 GHz).

The development of pulse radars of a second type is underway for thepurpose of assistance at the time of low speed running such asautomobile dead angle assistance or assistance of putting a car ingarage by investigating a wide angle range with low output and in longdistance using a quasi millimeter wave (22 GHz to 29 GHz).

The quasi millimeter band for use in the pulse radars of this secondtype is generally referred to as an UWB (Ultra-wideband), and is usedfor medical radars, radars for walk assistance of visually handicappedpersons, or a short distance communication system or the like as well asautomotive radars.

The UWB is a wide bandwidth, and thus, in a radar system, a short pulsehaving a width shorter than 1 ns can be used, and it is expected thatshort range radars having high distance resolution can be achieved.

DISCLOSURE OF INVENTION

However, in actuality, there are a variety of problems to be solved,which will be described later, in order to achieve short range radarshaving high distance resolution using this UWB.

One of the important problems is that, although there is a need fordownsizing and low power consumption in incorporation of automotiveradars into a variety of vehicles or portable use of radars for walkassistance of visually handicapped persons, conventional pulse radarscannot respond to such a need sufficiently.

That is, from the fact that phase information can be obtained by areceiver section 12 of the conventional pulse radars, a quadrature typedetector circuit is used as a detector circuit 13.

This quadrature type detector circuit 13, as shown in FIG. 15, branchesan input signal S in phase by means of a distributor 13 a, and inputsthe branched signals to two mixers 13 b and 13 c, respectively.

Here, a local signal L is inputted to the two mixers 13 b and 13 c,respectively, after divided into signals each having a 90-degree phasedifference by means of a 90-degree distributor 13 d.

Then, the two mixers 13 b and 13 c mix the input signal S with the localsignal L divided into the signals each having a 90-degree phasedifference.

The local signal L is used to branch a part of the pulse waves(transmission waves) from the transmitter section 11 shown in FIG. 14,for example.

Then, two filters 13 e and 13 f sample baseband components I and Q fromthe output components from the two mixers 13 b and 13 c.

A computing process for these baseband components I and Q is carried outby means of a signal processor section 15 shown in FIG. 14 afterprocessed via a sample hold circuit or an A/D converter and the like,although not shown, for example, thereby making it possible to graspstrength and a phase of an input signal S, i.e., a reflection wave Prfrom the object 1 a shown in FIG. 14.

Hence, such a quadrature type detector circuit 13 not only requires twomixers 13 b and 13 c but also requires two systems such as a circuitthat follows these mixers, such as a sample hold circuit or an A/Dconverter, for example, and there is a problem that an equipmentconstruction of the pulse radars becomes complicated, resulting inhigher cost.

Further, the quadrature type detector circuit 13 requires an amplifieror the like because there is a need for supplying a local signal withsufficient power to the two mixers 13 b and 13 c, and there is a problemthat a whole equipment construction of pulse radars becomes complicated,resulting in high power consumption.

In addition, a 90-degree distributor 13 d in a quasi millimeter band isproper in a circular “rat race” type because of its distributionconstant type and a small loss.

Hence, there is a problem that this “rat race” type structured 90-degreedistributor 13 d is hardly hybridized with an IC circuit, and a circuitconstruction becomes large-sized.

In addition, a frequency of a local signal L for use in the quadraturetype detector circuit 13 is a receiving frequency itself, and moreover,is at a high level, as described above. Thus, there is a need for heavyshielding so as to prevent the cable run or receiving of the leakcomponent. Therefore, there is a problem that equipment downsizingbecomes difficult.

On the other hand, it is possible to consider use of a peak detectorcircuit with a diode used in power measurement or the like instead ofusing the quadrature type detector circuit with its complicatedconstruction and high power consumption as described above.

Hence, the peak detector circuit with a diode is low in response speedin principle, and cannot detect a receiving signal having a short pulseof 1 ns or less as described above.

In addition, in the case where a target serving as an object 1 a has ahigh reflection factor such as a metal plate, a transmission pulsewaveform is analogous to a receiving waveform reflected and returnedfrom the target.

In this case, as described previously, the quadrature type detectorcircuit 13 used as a local signal by branching a transmission wave isemployed as a detector circuit, a correlation of a detected output isobtained by means of a signal processor section 15, thereby making itpossible to detect a target with high sensitivity.

Hence, with respect to a target having dispersion property such as ahuman body, even if the quadrature type detector circuit 13 is employedas a detector circuit, a receiving pulse has a long tail, and itswaveform is different from an ideal waveform. Thus, there is a problem acorrelation output becomes small, and a radars sensing capability islowered.

The present invention has been made in order to solve theabove-described problems associated with the conventional technique. Itis an object of the present invention to provide short range radars anda method for controlling the short range radars which are available inUWB, small sized, and low in power consumption.

In order to achieve the above-described objects, according to a firstaspect of the present invention, there is provided a short range radarcomprising: a transmitter section (21) which radiates a short range wave(Pt) to a space (1); a receiver section (30) having a detector circuit(33) composed of a branch circuit (34) which receives a reflection wave(Pr) of the short range wave (Pt) radiated to the space (1) by means ofthe transmitter section (21) and branches in phase a signal (R′) of thereflection wave (Pr) into first and second signals (V1, V2), a linearmultiplier (35) which linearly multiplies the first and second signals(V1, V2) branched in phase by means of the branch circuit (34), and alow pass filter (36) which samples a baseband component from an outputsignal from the linear multiplier (35); a signal processor section (40)which carries out an analyzing process of an object (1 a) which existsin the space (1) based on an output from the receiver section (30); anda control section (50) which makes a predetermined control with respectto at least one of the transmitter section (21) and the receiver section(30) based on an analysis result from the signal processor section (40).

In order to achieve the above-described objects, according to a secondaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein the linear multiplier(35) of the detector circuit (33) is composed of a Gilbert mixer.

In order to achieve the above-described objects, according to a thirdaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein the receiver section(30) has a sample hold circuit (37) which carries out integration withrespect to an output signal of the detector circuit (33) and holds andoutputs a result of the integration.

In order to achieve the above-described objects, according to a fourthaspect of the present invention, there is further provided the shortrange radar according to the third aspect, wherein the control section(50) variably controls an integration start timing and an integrationtime of the sample hold circuit (37) based on a processing result fromthe signal processor section (40).

In order to achieve the above-described objects, according to a fifthaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein a plurality of samplehold circuits (37A, 37B, 37C, 37D) are provided as the sample holdcircuit (37), and the plurality of sample hold circuits (37A, 37B, 37C,37D) each carry out integration in different periods from each otherwith respect to the output signal from the detector circuit (33).

In order to achieve the above-described objects, according to a sixthaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein a power amplifier(25) which amplifies the short range wave (Pt) is provided at thetransmitter section (21), a low noise amplifier (32) which amplifies asignal of the reflection wave (Pr) is provided at the receiver section(30), and the control section (50) controls a gain of at least one ofthe power amplifier (25) provided at the transmitter section (21) andthe low noise amplifier (32) provided at the receiver section (30) sothat a signal level (R′) of the reflection wave (Pr) inputted to thedetector circuit (33) at the receiver section (30) is within a linearoperation range of the linear multiplier.

In order to achieve the above-described objects, according to a seventhaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein the transmittersection (21) is provided with: a pulse generator (23) which generates apulse signal (Pa) having a predetermined width; and an oscillator (24)which operates to oscillate only in a period in which the pulse signal(Pa) from the pulse generator (23) is inputted and outputs an outputsignal (Pb) as the short range wave (Pt), and stops the oscillatingoperation in a period in which the pulse signal (Pa) is not inputted.

In order to achieve the above-described objects, according to an eighthaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein the control section(50) stops power supply to the transmitter section (21) in a period inwhich the transmitter section (21) radiates the short range wave (Pt) tothe space (1), and radiates a next short range wave (Pt) to the space(1).

In order to achieve the above-described objects, according to a ninthaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein the control section(50) stops power supply to the receiver section (30) in a period inwhich the transmitter section (21) radiates the short range wave (Pt) tothe space (1), and then, radiates a next short range wave (Pt) to thespace (1) except a period in which a reflection wave (Pr) relevant tothe short range wave (Pt) radiated to the space (1) is received by meansof the receiver section (30).

In order to achieve the above-described objects, according to a tenthaspect of the present invention, there is further provided the shortrange radar according to the first aspect, wherein first and secondreceiver sections (30A, 30B) are provided as the receiver section (30),each of which has first and second receiving antennas (31A, 31B)provided to be spaced from each other with a predetermined distance inorder to receive the reflection wave (Pr), and the signal processorsection (40) analyzes a direction of an object (1 a) which exists in thespace (1) based on output signals from the first and second receiversections (30A, 30B).

In order to achieve the above-described objects, according to aneleventh aspect of the present invention, there is further provided theshort range radar according to the second aspect, wherein the Gilbertmixer used as the linear multiplier (35) of the detector circuit (33)comprises: a first differential amplifier (35 a) comprising first andsecond transistors (Q1, Q2) each having a base input end, a collectoroutput end, and an emitter common current path, the emitter commoncurrent path of the first and second transistors (Q1, Q2) beingconnected to a constant current source (I1); a second differentialamplifier (35 b) comprising third and fourth transistors (Q3, Q4) eachhaving a base input end, a collector output end, and an emitter commoncurrent path, the emitter common current path of the third and fourthtransistors (Q3, Q4) being connected to a collector output end of thefirst transistor (Q1) of the first differential amplifier (35 a); athird differential amplifier (35 c) comprising fifth and sixthtransistors (Q5, Q6) each having a base input end, a collector outputend, and an emitter common current path, the base input end of the fifthtransistor (Q5) being connected in common to the base input end of thefourth transistor (Q4) of the second differential amplifier (35 b), theemitter common current path of the fifth and sixth transistors (Q5, Q6)being connected to a collector output end of the second transistor (Q2)of the first differential amplifier (35 a); a first load resistor (R3)and a first output end (OUT1) connected in common to a collector outputend of the third transistor (Q3) of the second differential amplifier(35 b) and a collector output end of the fifth transistor (Q5) of thethird differential amplifier (35 c), respectively; a second loadresistor (R4) and a second output end (OUT2) connected in common to acollector output end of the fourth transistor (Q4) of the seconddifferential amplifier (35 b) and a collector output end of the sixthtransistor (Q6) of the third differential amplifier (35 c),respectively; a first low pass filter (LPF1) including first and secondcoils (L1, L2) and a first resistor (R9) and a second low pass filter(LPF2) including third and fourth coils (L3, L4) and a second resistor(R10) connected in series, respectively, between a first pair of lines(+, −) and an earth line which transmits the first signal (V1) branchedin phase by means of the branch circuit (34); a third low pass filter(LPF3) including fifth and sixth coils (L5, L6) and a third resistor(R11) and a fourth low pass filter (LPF4) including seventh and eighthcoils (L7, L8) and a fourth resistor (R12) connected in series,respectively, between a second pair of lines (+, −) and an earth linewhich transmits the second signal (V2) branched in phase by means of thebranch circuit (34); first and second emitter follower circuits (EF1,EF2) comprising seventh and eighth transistors (Q7, Q8) each having abase input end and an emitter output end, the base input ends of theseventh and eighth transistors (Q7, Q8) each being connected to each ofconnecting neutral points of the first and second coils (L1, L2) and thethird and fourth coils (L3, L4) as each of the output ends of the firstand second low pass filters (LPF1, LPF2); third and fourth emitterfollower circuits (EF3, EF4) comprising ninth and tenth transistors (Q9,Q10) each having a base input end and an emitter output end, the baseinput ends of the ninth and tenth transistors (Q9, Q10) each beingconnected to each of connecting neutral points of the fifth and sixthcoils (L5, L6) and the seventh and eighth coils (L7, L8) as each of theoutput ends of the third and fourth low pass filters (LPF3, LPF4); afifth low pass filter (LPF5) composed of: a ninth coil (L9) connectedbetween a common collector output end of the third transistor (Q3) ofthe second differential amplifier (35 b) and the fifth transistor (Q5)of the third differential amplifier (35 c) and the first load resistor(R3); a tenth coil (L10) connected between the common collector outputend of the third transistor (Q3) of the second differential amplifier(35 b) and the fifth transistor (Q5) of the third differential amplifier(35 c) and the first output end (OUT1); and the first load resistor(R3); and a sixth low pass filter (LPF6) composed of: an eleventh coil(L11) connected between a common collector output end of the fourthtransistor (Q4) of the second differential amplifier (35 b) and thesixth transistor (Q6) of the third differential amplifier (35 c) and thesecond load resistor (R4); a twelfth coil (L12) connected between acommon collector output end of the fourth transistor (Q4) of the seconddifferential amplifier (35 b) and the sixth transistor (Q6) of the thirddifferential amplifier (35 c) and the second output end (OUT2); and thesecond load resistor (R4), wherein each of the base input ends of thefirst and second transistors (Q1, Q2) of the first differentialamplifier (35 a) is connected to each of the output ends of the firstand second emitter follower circuits (EF1, EF2), respectively, andthereby the first signal (V1) branched in phase by means of the branchcircuit (34) is inputted to the first differential amplifier (35 a); andeach of the base input ends of the third transistor (Q3) of the seconddifferential amplifier (35 b) and the sixth transistor (Q6) of the thirddifferential amplifier (35 c) is connected to each of the output ends ofthe third and fourth emitter follower circuits (EF3, EF4), respectively,and thereby the second signal (V2) branched in phase by means of thebranch circuit (34) is inputted to the second and third differentialamplifiers (35 b, 35 c), and thereby a linearly multiplied outputs ofthe first and second signals (V1, V2) can be led out from at least oneof the first and second output ends (OUT1, OUT2).

In order to achieve the above-described objects, according to a twelfthaspect of the present invention, there is provided a short range radarcontrolling method comprising the steps of: preparing a transmittersection (21), a receiver section (30), and a linear multiplier (35);radiating a short range wave (Pt) to a space (1) by means of thetransmitter section (21); receiving a reflection wave (Pr) of the shortrange wave (Pt) radiated to the space (1) by means of the receiversection (30) to branch in phase a signal (R′) of the reflection wave(Pr) into first and second signals (V1, V2); linearly multiplying thefirst and second signals (V1, V2) by means of the linear multiplier (35)to output a linearly multiplied signal; sampling a baseband componentfrom an output signal of the linear multiplier; carrying out ananalyzing process of an object (1 a) which exists in the space (1) basedon the baseband component; and making a predetermined control withrespect to at least one of the transmitter section (21) and the receiversection (30) based on a result of the analyzing process.

In order to achieve the above-described objects, according to athirteenth aspect of the present invention, there is further providedthe short range radar controlling method according to the twelfthaspect, wherein the step of outputting the linearly multiplied signalcomprises the step of carrying out linear multiplication for outputtingthe linearly multiplied signal by using a Gilbert mixer as the linearmultiplier (35).

In order to achieve the above-described objects, according to afourteenth aspect of the present invention, there is further providedthe short range radar controlling method according to the twelfthaspect, further comprising the step of, before the step of carrying outthe analyzing process, carrying out integration with respect to thebaseband component and holding and outputting a result of theintegration.

In order to achieve the above-described objects, according to afifteenth aspect of the present invention, there is further provided theshort range radar controlling method according to the fourteenth aspect,wherein the step of carrying out integration with respect to thebaseband component comprises the step of variably controlling a starttiming of integration and an integration time with respect to thebaseband component based on the result of the analyzing process.

In order to achieve the above-described objects, according to asixteenth aspect of the present invention, there is further provided theshort range radar controlling method according to the fourteenth aspect,wherein the step of carrying out integration with respect to thebaseband component comprises the step of carrying out integration in aplurality of periods different from each other with respect to thebaseband component by using a plurality of sample hold circuits (37).

In order to achieve the above-described objects, according to aseventeenth aspect of the present invention, there is further providedthe short range radar controlling method according to the twelfthaspect, wherein a power amplifier (25) which amplifies the short rangewave (Pt) is provided at the transmitter section (21), a low noiseamplifier (32) which amplifies a signal (R) of the reflection wave (Pr)is provided at the receiver section (30), and the step of making thepredetermined control comprises a step of controlling a gain of at leastone of the power amplifier (25) provided at the transmitter section (21)and the low noise amplifier (32) provided at the receiver section (30)so that a signal (R′) level of the reflection wave (Pr) at the receiversection (30) is within a linear operation range of the linear multiplier(35).

In order to achieve the above-described objects, according to aneighteenth aspect of the present invention, there is further providedthe short range radar controlling method according to the twelfthaspect, wherein the step of radiating a short range wave (Pt) to a space(1) by means of the transmitter section (21) comprises the steps of:generating a pulse signal (Pa) having a predetermined width; making anoscillation operation only in a period in which the pulse signal (Pa) isinputted to output an output signal (Pb) as the short range wave (Pt);and stopping an oscillation operation during a period in which the pulsesignal (Pa) is not inputted so as not to output an output signal (Pb) asthe short range wave (Pt).

In order to achieve the above-described objects, according to anineteenth aspect of the present invention, there is further providedthe short pulse radar controlling method according to the twelfthaspect, wherein the step of making the predetermined control comprisesthe step of: stopping power supply to the transmitter section (21) in aperiod in which the transmitter section (21) radiates the short rangewave (Pt) to the space (1), and then, radiates a next short range wave(Pt) to the space (1).

In order to achieve the above-described objects, according to atwentieth aspect of the present invention, there is further provided theshort range radar controlling method according to the twelfth aspect,wherein the step of making the predetermined control comprises the stepof; stopping power supply to the receiver section (30) in a period inwhich the transmitter section (21) radiates the short range wave (Pt) tothe space (1), and then, radiates a next short range wave (Pt) to thespace (1) except a period in which a reflection wave (Pr) with respectto the short range wave (Pt) radiated to the space (1) is received bymeans of the receiver section (30).

In order to achieve the above-described objects, according to atwenty-first aspect of the present invention, there is further providedthe short range radar controlling method according to the twelfthaspect, wherein first and second receiver sections (30A, 30B) areprovided as the receiver section (30), each of which has first andsecond receiving antennas (31A, 31B) provided to be spaced from eachother with a predetermined distance in order to receive the reflectionwave (Pr), and the step of carrying out the analyzing process comprisesthe step of analyzing a direction of an object (1 a) which exists in thespace (1) based on output signals from the first and second receiversections (30A, 30B).

In order to achieve the above-described objects, according to atwenty-second aspect of the present invention, there is further providedthe short range radar controlling method according to the twelfthaspect, wherein, in the step of outputting the linearly multipliedsignal, the Gilbert mixer used as the linear multiplier (35) comprises:a first differential amplifier (35 a) comprising first and secondtransistors (Q1, Q2) each having a base input end, a collector outputend, and an emitter common current path, the emitter common current pathof the first and second transistors (Q1, Q2) being connected to aconstant current source (I1); a second differential amplifier (35 b)comprising third and fourth transistors (Q3, Q4) each having a baseinput end, a collector output end, and an emitter common current path,the emitter common current path of the third and fourth transistors (Q3,Q4) being connected to a collector output end of the first transistor(Q1) of the first differential amplifier (35 a); a third differentialamplifier (35 c) comprising fifth and sixth transistors (Q5, Q6) eachhaving a base input end, a collector output end, and an emitter commoncurrent path, the base input end of the fifth transistor (Q5) beingconnected in common to the base input end of the fourth transistor (Q4)of the second differential amplifier (35 b), the emitter common currentpath of the fifth and sixth transistors (Q5, Q6) being connected to acollector output end of the second transistor (Q2) of the firstdifferential amplifier (35 a); a first load resistor (R3) and a firstoutput end (OUT1) connected in common to a collector output end of thethird transistor (Q3) of the second differential amplifier (35 b) and acollector output end of the fifth transistor (Q5) of the thirddifferential amplifier (35 c), respectively; a second load resistor (R4)and a second output (OUT2) end connected in common to a collector outputend of the fourth transistor (Q4) of the second differential amplifier(35 b) and a collector output end of the sixth transistor (Q6) of thethird differential amplifier (35 c), respectively; a first low passfilter (LPF1) including first and second coils (L1, L2) and a firstresistor (R9) and a second low pass filter (LPF2) including third andfourth coils (L3, L4) and a second resistor (R10) connected in series,respectively, between a first pair of lines (+, −) and an earth linewhich transmits the first signal (V1) branched in phase by means of thebranch circuit (34); a third low pass filter (LPF3) including fifth andsixth coils (L5, L6) and a third resistor (R11) and a fourth low passfilter (LPF4) including seventh and eighth coils (L7, L8) and a fourthresistor (R12) connected in series, respectively, between a second pairof lines (+, −) and an earth line which transmits the second signal (V2)branched in phase by means of the branch circuit (34); first and secondemitter follower circuits (EF1, EF2) comprising seventh and eighthtransistors (Q7, Q8) each having a base input end and an emitter outputend, the base input ends of the seventh and eighth transistors (Q7, Q8)each being connected to each of connecting neutral points of the firstand second coils (L1, L2) and the third and fourth coils (L3, L4) aseach of the output ends of the first and second low pass filters (LPF1,LPF2); third and fourth emitter follower circuits (EF3, EF4) comprisingninth and tenth transistors (Q9, Q10) each having a base input end andan emitter output end, the base input ends of the ninth and tenthtransistors (Q9, Q10) each being connected to each of connecting neutralpoints of the fifth and sixth coils (L5, L6) and the seventh and eighthcoils (L7, L8) as each of the output ends of the third and fourth lowpass filters (LPF3, LPF4); a fifth low pass filter (LPF5) composed of: aninth coil (L9) connected between a common collector output end of thethird transistor (Q3) of the second differential amplifier (35 b) andthe fifth transistor (Q5) of the third differential amplifier (35 c) andthe first load resistor (R3); a tenth coil (L10) connected between thecommon collector output end of the third transistor (Q3) of the seconddifferential amplifier (35 b) and the fifth transistor (Q5) of the thirddifferential amplifier (35 c) and the first output end (OUT1); and thefirst load resistor (R3); and a sixth low pass filter (LPF6) composedof: an eleventh coil (L11) connected between a common collector outputend of the fourth transistor (Q4) of the second differential amplifier(35 b) and the sixth transistor (Q6) of the third differential amplifier(35 c) and the second load resistor (R4); a twelfth coil (L12) connectedbetween the common collector output end of the fourth transistor (Q4) ofthe second differential amplifier (35 b) and the sixth transistor (Q6)of the third differential amplifier (35 c) and the second output end(OUT2); and the second load resistor (R4), wherein

each of the base input ends of the first and second transistors (Q1, Q2)of the first differential amplifier (35 a) is connected to each of theoutput ends of the first and second emitter follower circuits (EF1,EF2), respectively, and thereby the first signal (V1) branched in phaseby means of the branch circuit (34) is inputted to the firstdifferential amplifier (35 a),

each of the base input ends of the third transistor (Q3) of the seconddifferential amplifier (35 b) and the sixth transistor (Q6) of the thirddifferential amplifier (35 c) is connected to each of the output ends ofthe third and fourth emitter follower circuits (EF3, EF4), respectively,and thereby the second signal (V2) branched in phase by means of thebranch circuit (34) is inputted to the second and third differentialamplifiers (35 b, 35 c), and thereby a linearly multiplied outputs ofthe first and second signals (V1, V2) can be led out from at least oneof the first and second output ends (OUT1, OUT2).

With the above-described construction, according to short range radarsand controlling method thereof of the present invention, a detectorcircuit multiplies signals obtained by branching received reflectionwave signals by a branch circuit by means of a linear multiplier toobtain its square component, and samples a baseband component from itssquare component by means of a filter, thereby detecting a reflectionwave signal. Thus, there is no need for a local signal for detection,and concurrently, its construction is simplified, making it possible tocontribute to achievement of short range radars which are small in sizeand low in power consumption.

In addition, the short range radars and controlling method thereof ofthe present invention is a system of integrating power of received wavesunlike a conventional correlating process, and thus, is suitable fordetecting a target having a so-called large dispersion property in whicha transmission pulse and a receiving pulse are greatly different fromeach other in waveform, such as a human body.

Further, according to the short range radars and controlling methodthereof of the present invention, an oscillator for making anoscillating operation only during a period in which a pulse is inputtedand outputting a short range wave as a transmission wave is used in atransmitter section, thereby preventing the generation of the residualcarrier.

When a reflection wave signal is detected, there occurs a problem suchas unstable characteristics due to a transient response when a localsignal is intermittently generated, in the conventional quadraturedetecting system. However, the present invention is directed to a squaredetecting system whose detecting characteristics does not basicallydepend on a transmission waveform, and can be applied smoothly withoutany problem when the above-described reflection wave signal is detected.

That is, according to short range radars and control method thereof ofthe present invention, as described above, a short pulse generatingsystem and a square detecting system in which the residual carrier isnot generated are combined with each other, thereby making it possibleto contribute to achievement of short range radars suitable fordetection of a target having a variety of scattering characteristicswith a simple construction.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram depicting a system configuration of a firstembodiment of short range radars according to the present invention;

FIG. 2 is a block diagram depicting an example of a transmitter for usein a transmitter section of the short range radars according to thefirst embodiment shown in FIG. 1;

FIG. 3 is a view showing a pulse signal Pa of a cycle Tg inputted to atransmitter and a signal Pb formed in a rectangular shape outputted in aburst shape from the transmitter for the purpose of a description ofoperation of the transmitter shown in FIG. 2;

FIG. 4 is a block diagram depicting another example of a transmitter foruse in a transmitter section of the short range radars according to thefirst embodiment shown in FIG. 1;

FIG. 5A is a circuit schematic view depicting a basic type of a Gilbertmixer employed as an example of a linear multiplier of a detectorcircuit for use in a receiver section of the short range radarsaccording to the first embodiment shown in FIG. 1;

FIG. 5B is a circuit schematic view depicting an improved type of theGilbert mixer shown in FIG. 5A;

FIG. 6 is a view showing a sine wave shaped signal S (t) inputted in aburst shape in phase to the Gilbert mixer and a square wave S (t)² andits envelope (baseband) W outputted from the Gilbert mixer for thepurpose of a description of operation of the Gilbert mixer shown inFIGS. 5A and 5B;

FIG. 7 is a view showing a measurement result of frequencycharacteristics of a linear multiplier in the case where the Gilbertmixer shown in FIG. 5B is employed;

FIG. 8 is a view showing an observed waveform of a baseband component Wobtained when an output of the linear multiplier in response to an inputsignal of a pulse width 1 ns in the case where the Gilbert mixer shownin FIG. 5B is employed is subjected to a 7 GHz bandwidth limitation bymeans of a low pass filter;

FIG. 9 is a view showing a measurement result of input and outputcharacteristics of the linear multiplier in the case where the Gilbertmixer shown in FIG. 5B is employed;

FIG. 10 is a view showing a principal construction of a sample holdcircuit for use in a receiver section of the short range radarsaccording to the first embodiment shown in FIG. 1;

FIG. 11 is a timing chart adopted to explain an operation of the shortrange radars according to the first embodiment shown in FIG. 1;

FIG. 12 is a block diagram depicting a construction of essentialportions of a second embodiment of short range radars according to thepresent invention;

FIG. 13 is a block diagram depicting a construction of essentialportions of a third embodiment of short range radars according to thepresent invention;

FIG. 14 is a block diagram depicting a basic construction ofconventional pulse radars;

FIG. 15 is a block diagram depicting a basic construction of aquadrature type detector circuit for use in the conventional pulseradars shown in FIG. 14; and

FIG. 16 is a view showing a spectrum mask of a quasi millimeter waveband UWB and a desired use frequency band (recommended bandwidth).

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, some embodiments of short range radars according to thepresent invention will be described with reference to the accompanyingdrawings.

First Embodiment

First a description will be given with respect to a construction ofshort range radars according to a first embodiment of the presentinvention.

FIG. 1 is a block diagram depicting a construction of a short rangeradar 20 according to the first embodiment of the present invention.

The short range radar 20 according to the present invention basicallyincludes: a transmitter section 21 which radiates a short pulse Pt to aspace 1; a receiver section 30 having a detector circuit 33 composed ofa branch circuit 34 which receives a reflection wave Pr of a short rangewave Pt radiated to the space 1 by means of this transmitter section 21and branches in phase a signal R′ of the reflection wave Pr into firstand second signals V1 and V2, a linear multiplier 35 which linearlymultiplies the first and second signals V1 and V2 branched in phase bymeans of this branch circuit 34, and a low pass filter 36 which samplesa baseband component from an output signal from this linear multiplier35; a signal processor section 40 which carries out an analyzing processof an object 1 a which exists in the space 1 based on an output fromthis receiver section 30; and a control section 50 which makespredetermined control with respect to at least one of the transmittersection 21 and the receiver section 30 based on an analysis result fromthis signal processor section 40.

In addition, a method for controlling short range radars according tothe present invention basically includes the steps of: preparing thetransmitter section 21, the receiver section 30 and the linearmultiplier 35; radiating the short range wave Pt to the space 1 by thetransmitter section 21; receiving the reflection wave Pr of the shortrange wave Pt radiated to the space 1 by means of this receiver section30 and branching in phase the signal R′ of the reflection wave Pr intothe first and second signals V1 and V2; linearly multiplying the firstand second signals V1 and V2 by the linear multiplier 35 to output alinear multiplying signal; sampling a baseband component from thislinear multiplied output signal; carrying out an analyzing process ofthe object 1 a which exists in the space 1 based on this basebandcomponent; and making predetermined control with respect to at least oneof the transmitter section 21 and the receiver section 30 based on thisanalysis result.

Specifically, this short range radar 20 shown in FIG. 1 is composed ofthe transmitter section 21; the receiver section 30; an analog/digital(A/D) converter 30; the signal processor section 40; and the controlsection 50.

Every time the transmitter section 21 receives a trigger signal Goutputted from the control section 50 at a predetermined cycle Tg, thistransmitter section radiates to the space 1 via a transmitter antenna 22a short range wave Pt having a predetermined carrier frequency Fc (forexample, 26 GHz) at a predetermined bandwidth Tp (for example, 1 ns)generated as described later.

The transmitter antenna 22 may be shared with a receiver antenna 31 ofthe receiver section 30 described later.

This transmitter section 21, as shown in FIG. 1, has: a pulse generator23 which generates a pulse signal Pa having a bandwidth Tp synchronizedwith a trigger signal G from the control section 50; an oscillator 24which oscillates and outputs a signal having a predetermined carrierfrequency Fc in a duration Tp in which a pulse signal Pa is receivedfrom this pulse generator 23; a power amplifier 25 which amplifies anoutput signal from this oscillator 24; a band rejection filter (BRF) 26which suppresses a out-of-bandwidth unnecessary radiation in response toan output signal from this power amplifier 25; and the transmitterantenna 22 to which a signal having passed through this BRF 26 issupplied as a transmission wave.

Here, some configurations of the oscillator 24 are considered.

FIG. 2 is a block diagram depicting an example of a configuration of theoscillator 24 for use in the transmitter section 21 of the short rangeradars according to the first embodiment shown in FIG. 1.

That is, this oscillator 24, as shown in FIG. 2, has: a 2-input,2-output type gate circuit 24 a in which common input AND and NANDcircuits are integrated with each other; first and second input buffers24 b and 24 c of emitter follower type connected to an input section ofthis gate circuit 24 a; and a delay circuit 24 e which delays by apredetermined delay time inverted outputs of an output buffer 24 dconnected to an output section of the gate circuit 24 a and the gatecircuit 24 a and inputs the delayed inverted outputs to the first inputbuffer 24 b.

This delay circuit 24 e is composed of a strip line or the like, forexample.

From the thus configured oscillator 24, as shown in FIG. 3A, while apulse signal Pa having a cycle Tg is inputted to the input buffer 24 c,as shown in FIG. 3B, a rectangular wave signal Pb having a predeterminedfrequency (carrier frequency) is oscillated and outputted in a burstshape.

A frequency of an output signal Pb from this oscillator 24 is determineddepending on a total of a delay time between an input and an output ofthe input buffer 24 b and the gate circuit 24 a and a delay time of thedelay circuit 24 e.

Here, the delay time between an input and an output of the input buffer24 b and the gate circuit 24 a is a fixed value generally determineddepending on a circuit device.

Therefore, a construction is provided so as to vary some of theconstants of the delay circuit 24 e, and these constants are adjusted,and thereby an oscillation frequency of the output signal Pb of theoscillator 24 is set at a substantially center frequency (for example,26 GHz) of the UWB.

FIG. 4 is a block diagram depicting another example of a configurationof the oscillator 24 for use in the transmitter section 21 of the shortrange radars according to the first embodiment shown in FIG. 1.

That is, the oscillator 24 according to this example of configuration,as shown in FIG. 4, has an amplifier 24 f; a resonator 24 g serving as aload of this amplifier 24 f; and a feedback circuit 24 h whichpositively feeds back an output of the amplifier 24 f to an input sideto form an oscillator circuit which operates to oscillate at a resonancefrequency (for example, 26 GHz) of the resonator 24 g.

Further, in this oscillator 24 according to this example ofconfiguration, a switch 24 i, the switching operation of which can becontrolled by means of a pulse signal Pa, is provided between an inputside (or output side) of the amplifier 24 f and an earth line.

This oscillator 24 according to this example of configuration operatesto oscillate when the switch 24 i is opened in a duration in which apulse signal Pa is inputted. In addition, in a duration in which nopulse signal Pa is inputted, the switch 24 i is closed, and one end of afeedback loop is short-circuited in an earth line, and thereby anoscillation operation stops.

Here, a configuration is provided such that short-circuit and openingare established between an input side of the amplifier 24 f and theearth line by means of the switch 24 i.

Hence, a configuration may be provided such that short-circuit andopening are established between an output side of the amplifier 24 f andthe earth line by means of the switch 24 i.

The transmitter section 21 using the oscillator 24 according to any ofthese configurations shown in FIGS. 2 and 4 is configured to control anoscillating operation itself of the oscillator 24 by means of a pulsesignal Pa. Thus, no carrier leakage occurs in principle.

Therefore, when an UWB is used, limitation of power density regulated asdescribed later may be considered only with respect to momentary powerof a short range wave outputted at the time of oscillation. Thus,transmission wave power can be efficiently used to the maximum within alimit of power density regulated in accordance with a UWB standardconcurrently because no carrier leakage occurs.

The above-described configurations of the oscillator 24 shown in FIGS. 2and 4 each are provided as an example. With another circuitconfiguration, for example, by turning on and off power (current sourceor the like) of an oscillator circuit in response to a pulse signal Paas well, a burst wave free of carrier leakage as described above can beobtained.

In order to obtain this burst wave, conventionally, there is used anamplification shift keying (ASK) system for pulse-modulating (ON/OFF) a24 GHz carrier signal (continuous wave) by using a switch.

Hence, in such a conventional ASK system, isolation at the time ofswitching OFF is not complete, and a carrier leakage occurs. Moreover,in short range radars, an OFF time is overwhelmingly longer by severalthousand times to several ten thousand times than ON time (for example 1ns). Thus, even if a slight carrier leakage occurs, the large residualcarrier power is generated as a whole.

This residual carrier limits substantial receiving sensitivity of areflection wave with respect to a transmission wave of short rangeradars, thus narrowing a radar investigation range and making itdifficult to detect an obstacle having a low reflection factor.

In addition, with respect to the UWB radar system, FCC (FederalCommunication Committee) regulates in the following non-patent document1 that average power density in a bandwidth of 22 GHz to 29 GHz be −41dBm/MHz or less, and peak power density be 0 dBm/50 MHz or less.

Non-patent document 1 FCC02-08, New Part 15 Rules, “FIRST REPORT ANDORDER”

Namely, in the above-described UWB radar system, a total amount ofenergy in the bandwidth of 22 GHz to 29 GHz is regulated. Thus, if theresidual carrier is large, an output level of a transmission wave mustbe set to be low concurrently, and an investigation distance or the likeis greatly limited.

In order to solve this problem, as indicated by dashed line from an UWBrecommended bandwidth indicated by solid line in FIG. 16, a centerfrequency of the transmission wave of short range radars is saved to aband having a narrow bandwidth (Short Range Device: SRD) from 24.05 GHzto 24.25 GHz allocated for Doppler radars, and thereby it is consideredthat regulations on the residual carrier by FCC can be avoided.

However, in this case, as shown in FIG. 16, there is a radiationrestricted band by RR (International Radio Communication Rules) forprotecting a passive sensor of EESS (Earth Survey Satellite) near SRD,and serious interference with this radiation restricted band is aninterest of concern.

In contrast, in the present invention, as described above, a system ofcontrolling ON/OFF an oscillating operation itself by means of a pulsesignal Pa to principally prevent the generation of the residual carrieris employed as a configuration of the oscillator 24, and thereby afrequency of a radar transmission wave can be freely set within arecommended bandwidth of a spectrum mask regulated as shown in FIG. 16.

Moreover, in the present invention, the frequency of the transmissionwave can be set so as to sufficiently avoid interference with theradiation restricted band as described above.

A signal Pb outputted from the oscillator 24 as described above isamplified by means of the power amplifier 25, and the amplified signalis supplied to the transmitter antenna 22 as a short range wave Pthaving a predetermined carrier frequency Fc (for example, 26 GHz) viathe BRF 26.

In this manner, from the transmitter antenna 22, the short range wave Ptis radiated to the space 1 targeted for investigation.

A gain of the power amplifier 25 can be variably controlled by means ofthe control section 50.

On the other hand, the receiver section 30 receives a reflection wave Prfrom the object 1 a of the space 1 via the receiving antenna 31;amplifies a signal R of the reflection Pr by means of an LNA (Low NoiseAmplifier) 32; and then, detects by means of a detector circuit 33 asignal R′ of the reflection wave Pr bandwidth-limited by means of a bandpass filter (BPF) 41 having a bandwidth of about 2 GHz.

A gain of the LNA32 can be variably controlled by means of the controlsection 50.

The detector circuit 33 is composed of: the branch circuit 34 whichbranches the signal R′ of the reflection wave Pr outputted from the BRF41 into the first signal V1 and the second signal V2 in phase (0degree); the linear multiplier 35 which linearly multiplies the signalsbranched into two signals in that phase, i.e., the first signal V1 andthe second signal V2; and a low pass filter (LPF) 36 which samples abaseband component W from an output signal of this linear multiplier 36.

The linear multiplier 35 includes some systems such as use of a doublebalancing mixer, and a method for configuring the multiplier by using aGilbert mixer is considered as that which operates at a high speed.

This Gilbert mixer, as shown in FIG. 5A, basically consists of first tothird differential amplifiers 35 a, 35 b, and 35 c.

Then, the first signal V1 is differentially inputted to a firstdifferential amplifier 35 a and the second signal V2 is differentiallyinputted to second and third differential amplifiers 35 b and 35 cconnected to a load side of this first differential amplifier 35 a. Inthis manner, only a linearly multiplied signal component—(V1×V2) of aninverted phase equal to a product of the first signal V1 and the secondsignal V2 and a linearly multiplied signal component (V1×V2) of apositive phase are outputted from common load resistors R3 and R4 of thesecond and third differential amplifiers 35 b and 35 c.

Specifically, in this Gilbert mixer, the first differential amplifier 35a includes first and second transistors Q1 and Q2 each having a baseinput end, a collector output end, and an emitter common current path,wherein each of the base input ends of the first and second transistorsQ1 and Q2 is connected to a first signal source V1 and the emittercommon current path is connected to an earth line in series via aconstant current source I1 and a first bias power source Vb1.

The emitter common current path of the first and second transistors Q1and Q2 is lead out from a connection neutral point of emitter resistorsR1 and R2 and a base input end of the second transistor Q2 is connectedto an earth line via a second bias power source Vb2.

In addition, the second differential amplifier 35 b includes third andfourth transistors Q3 and Q4 each having a base input end, a collectoroutput end, and an emitter common current path, wherein each of the baseinput ends of the third and fourth transistors Q3 and Q4 is connected toa second signal source V2 and the emitter common current path of thethird and fourth transistors Q3 and Q4 is connected to the collectoroutput end of the first transistor Q1 of the first differentialamplifier 35 a.

In addition, the third differential amplifier 35 a includes fifth andsixth transistors Q5 and Q6 each having a base input end, a collectoroutput end, and an emitter common current path, wherein each of the baseinput ends of the fifth and sixth transistors Q5 and Q6 is connected tothe second signal source V2 and the emitter common current path of thefifth and sixth transistors Q5 and Q6 is connected to the collectoroutput end of the second transistor Q2 of the first differentialamplifier 35 a.

The base input end of each of the fourth transistor Q4 of the seconddifferential amplifier 35 b and the fifth transistor Q5 of the thirddifferential amplifier 35 c is connected in common, and is connected toan earth line via a third bias power source Vb3.

In addition, a collector output end of the third transistor Q3 of thesecond differential amplifier 35 b and a collector output end of thefifth transistor Q5 of the third differential amplifier 35 c areconnected to an earth line via a load resistor R3 in common, and isconnected to a first output end OUT1.

In addition, a collector output end of the fourth transistor Q4 of thesecond differential amplifier 35 b and a collector output end of thesixth transistor Q6 of the third differential amplifier 35 c areconnected to an earth line via a load resistor R4 in common, and isconnected to a second output end OUT2.

In this manner, at least one of the linearly multiplied outputs—(V1×V2)and (V1×V2) of the first and second signals V1 and V2 can be lead outfrom the first and second output ends OUT1 and OUT2.

As the first and second signals V1 and V2, when a sine wave shapedsignal S (t) as shown in FIG. 6A, for example, is inputted to the thusconfigured linear multiplier 35 using the Gilbert mixer in a burst shapein phase, the output signal is produced as a waveform (S (t)²) obtainedby squaring the input signal S (t), as shown in FIG. 6B, and theenvelope (baseband) W is proportional to power of the input signal S(t).

In this way, the linear multiplier 35 using the Gilbert mixer whichconsists of a plurality of differential amplifiers for use in thedetector circuit 33 can be configured to be very small-sized with amicrowave monolithic integrated circuit (MMC). Moreover, there is noneed for supplying a local signal unlike a conventional quadrature typedetector circuit, and thus, power consumption is reduced concurrently.

In the meantime, the response characteristics of the linear multiplier35 using the Gilbert mixer which has a basic circuit configuration asshown in FIG. 5A have a room to be improved for use in UWB.

Therefore, the inventors have improved its response characteristics bymaking improvement so as to carry out impedance matching or peakingcorrection and the like of an input/output section of a linearmultiplier using the Gilbert mixer which has a basic circuitconfiguration as shown in FIG. 5A, and has achieved a linear multiplierwhich can be fully used in UWB.

FIG. 5B shows a circuit configuration of a Gilbert mixer of improvedtype achieved by the inventors.

In FIG. 5B, like constituent elements of the Gilbert mixer having abasic circuit configuration shown in FIG. 5A are designated by likereference numerals. A duplicate description is omitted here.

That is, as shown in FIG. 5B, in the Gilbert mixer of improved type, anemitter common current path of the third and fourth transistors Q3 andQ4 of the second differential amplifier 35 b is lead out from aconnection neutral point of the emitter resistors R5 and R6. Inaddition, the emitter common current path of the fifth and sixthtransistors Q5 and Q6 of the third differential amplifier 35 c is leadout from a connection neutral point of the emitter resistors R7 and R8.

Although use of these pairs of emitter resistors R5 and R6, and R7 andR8 is desirable in principle, as in the emitter resistors R1 and R2 ofthe first and second transistors Q1 and Q2 of the first to thirddifferential amplifiers 35 a, not so serious problem occurs in an actualcircuit configuration even if they are eliminated.

In addition, in the Gilbert mixer of improved type as shown in FIG. 5B,first to fourth low pass filters LPF1, LPF2, LPF3, and LPF4 and first toforth emitter follower circuits EF1, EF2, EF3, and EF4 as described inthe following specific configuration are provided at input sections ofthe first to third differential amplifiers 35 a, 35 b, and 35 c.

In the Gilbert mixer of improved type as shown in FIG. 5B, fifth andsixth low pass filters LPF5 and LPF6 as described in the followingspecific configuration are provided at output sections of the second andthird differential amplifiers 35 b and 35 c.

That is, according to the specific configuration of the Gilbert mixer ofimproved type as shown in FIG. 5B, the first low pass filter LPF1including first and second coils L1 and L2 and a ninth resistor R9connected in series and the second low pass filter LPF2 including thirdand fourth coils L3 and L4 and a tenth resistor R10 are provided,respectively, between a first pair of lines + and − for transmitting afirst signal V1 branched in phase by means of the branch circuit 34 andan earth line.

In addition, in this Gilbert mixer of improved type, the third low passfilter LPF3 including fifth and sixth coils L5 and L6 and a eleventhresistor R11 connected in series and the fourth low pass filter LPF4including seventh and eighth coils L7 and L8 and a twelfth resistor R12are provided, respectively, between a second pair of lines + and − fortransmitting a second signal V2 branched in phase by means of the branchcircuit 34 and the earth line.

In addition, this Gilbert mixer of improved type includes seventh andeighth transistors Q7 and Q8 each having a base input end and an emitteroutput end. This mixer includes the first and second emitter followercircuits EF1 and EF2 in which each of the base input ends of the seventhand eighth transistors Q7 and Q8 is connected to each of the connectingneutral points of the first and second coils L1 and L2 and the third andfourth coils L3 and L4 as output ends of the first and second low passfilters LFP1 and LPF2.

In addition, this Gilbert mixer of improved type includes ninth andtenth transistors Q9 and Q10 each having a base input end and an emitteroutput end. This mixer includes third and fourth emitter followercircuits EF3 and EF4 in which each of the base input ends of the ninthand tenth transistors Q9 and Q10 is connected to each of the connectingneutral points of the fifth and sixth coils L5 and L6 and the seventhand eighth coils L7 and L8 as output ends of the third and fourth lowpass filters LFP3 and LPF4.

From among the first and second pairs of lines + and − for transmittingthe first and second signals V1 and V2, the second and third bias powersources Vb2 and Vb3 are connected between one line − and an earth line.

Here, in each of the emitters of the seventh and eighth transistors Q7and Q8 and the ninth and tenth transistors Q9 and Q10, thirteenth tosixteenth resistors are connected at a connecting neutral point betweenthe constant current source I1 and the bias power source Vb1,respectively.

In addition, each of the base input ends of the first and secondtransistors Q1 and Q2 of the first differential amplifier 35 a isconnected to each of the output ends of the first and second emitterfollower circuits EF1 and EF2.

In addition, each of the base input ends of the third and sixthtransistors Q1 and Q2 of the second and third differential amplifiers 35b and 35 c is connected to each of the output ends of the third andfourth emitter follower circuits EF3 and EF4.

In addition, a collector output end of the third transistor Q3 of thesecond differential amplifier 35 b and a collector output end of thefifth transistor Q5 of the third differential amplifier 35 c areconnected in common to a load resistor R3 via the ninth coil L9, and areconnected to the first output end OUT1 via the tenth coil L10.

Here, the ninth coil L9, the load resistor R3, and the tenth coil L10configure a fifth low pass filter LPF5.

In addition, a collector output end of the fourth transistor Q4 of thesecond differential amplifier 35 b and a collector output end of thesixth transistor Q6 of the third differential amplifier 35 c areconnected to an earth line via an eleventh coil L11 in common and via aload resistor R4, and are connected to the second output end OUT2 via atwelfth coil L12.

Here, the eleventh coil L11, the load resistor R4, and the twelfth coilL12 configure the sixth low pass filter LPF6.

In this manner, at least one of the linearly multiplied output —(V1×V2)and (V1×V2) of the first and second signals V1 and V2 can be lead outfrom the first and second output ends OUT1 and OUT2.

That is, a sine wave shaped signal S (t) as shown in FIG. 6A, forexample, is inputted in a burst shape in phase as first and secondsignals V1 and V2 to the thus configured improved linear multiplier 35using the Gilbert mixer shown in FIG. 5B, its output signal is producedas a waveform (S (t)²) obtained by squaring an input signal S (t), asshown in FIG. 6B. Its envelope (baseband) W is proportional to power ofthe input signal S (t) as is the case with the basic linear multiplier35 using the Gilbert mixer shown in FIG. 5A.

In addition, the linear multiplier 35 using the Gilbert mixer shown inFIG. 5B improved for use in the detector circuit 33 can be configured tobe very small sized with a microwave monolithic integrated circuit(MMC). Moreover, there is no need for supplying a local signal unlike aconventional quadrature type detector circuit, and thus, powerconsumption is reduced concurrently, as is the case with the basiclinear multiplier 35 using the Gilbert mixer shown in FIG. 5A.

Hence, in the improved Gilbert mixer shown in FIG. 5B configured asdescribed above, the first to fourth low pass filters LPF1, LPF2, LPF3,and LPF4 and the first to fourth emitter follower circuits EF1, EF2,EF3, and EF4 each having high Q are provided at input sections of thefirst to third differential amplifiers 35 a, 35 b, and 35 c. In thismanner, input impedance is enhanced, and a peaking effect is attained.

In addition, in the Gilbert mixer of improved type as shown in FIG. 5B,the fifth and sixth low pass filters LPF5 and LPF6 are provided atoutput sections of the second and third differential amplifiers 35 b and35 c, and thereby a peaking effect is attained.

In this manner, the Gilbert mixer of improved type as shown in FIG. 5Bis improved so as to enable impedance matching or peaking correction andthe like at an input/output section of the linear multiplier 35 usingthe Gilbert mixer having a basic circuit configuration as shown in FIG.5A. Thus, its response characteristics are effectively improved, and theimproved linear multiplier 35 using the Gilbert mixer which can be fullyused in UWB can be provided.

FIG. 7 shows a measurement result of frequency characteristics of thelinear multiplier 35 using the Gilbert mixer of improved type shown inFIG. 5B.

That is, according to the measurement result of the frequencycharacteristics of the linear multiplier 35 using the Gilbert mixer ofimproved type shown in FIG. 7, a bandwidth within −3 dB extends to about27 GHz, and it is determined that sufficient adaptability be provided toshort range radars whose UWB center is a carrier frequency (for example,26 GHz).

FIG. 8 shows a waveform (averaging number 64) in the case of observingby means of an observation oscilloscope a baseband component W obtainedby applying 7 GHz bandwidth limitation to an output relevant to an inputsignal having a pulse width 1 ns of the linear multiplier 35 using theGilbert mixer of improved type as shown in FIG. 5B by means of a lowpass filter 36.

That is, according to the observation waveform shown in FIG. 8, anaverage rise time obtained by a computing function of the observationoscilloscope is set to about 59 ps, and an average fall time is set toabout 36 ps (a fall time from 80% to 20%), and it is found thatextremely high speed response characteristics are provided.

FIG. 9 shows a measurement result of input/output characteristics of thelinear multiplier 35 using the Gilbert mixer of improved type as shownin FIG. 5B.

That is, according to a measurement result shown in FIG. 9, it is foundthat good linearity is obtained in a wide range from −30 dBm to −5 dBmin input level.

Therefore, the level of an input signal (V1, V2) is controlled in therange from −30 dBm to −5 dBm, and thereby an output of the improvedlinear multiplier 35 using the Gilbert mixer shown in FIG. 5B preciselyindicates power of the input signal.

In addition, a baseband signal W obtained by means of the detectorcircuit 33 as described above is inputted to a sample hold circuit 37.

The sample hold circuit 37, as its principle is shown in FIG. 10, has aconfiguration for inputting a baseband signal W via a switch 37 c to anintegrator circuit using a resistor 37 a and a capacitor 37 b.

While a pulse signal Pc from a pulse generator 38 is at a high level(may be at a low level), the switch 37 c is closed, and the basebandsignal W is integrated. When the pulse signal Pc is at a low level, theswitch 37 c is opened, and an integration result is held by means of thecapacitor 37 b.

While a description is given assuming that a sampling cycle of thesample hold circuit 37, i.e., a cycle of the pulse signal Pc, is equalto that of a trigger signal G, the sampling cycle may be an integermultiple of a cycle Tg of the trigger signal G.

The pulse generator 38 receives a signal G′ synchronized with thetrigger signal G (or trigger signal G itself), and delays by a timeinterval Td specified by the control section 50 in response to thesignal G. In addition, this pulse generator generates a pulse signal Pchaving a width Tc specified by the control section 50 and outputs thegenerated signal to the sample hold circuit 37.

A signal H held after integrated by the sample hold circuit 37 isconverted into a digital value by means of an A/D converter 39immediately after being held, and the converted digital value isinputted to the signal processor section 40.

The signal processor section 40 analyzes the object 1 a which exists inthe space 1 based on a signal H obtained at the receiver section 30;broadcasts its analysis result by an output device, although not shown(for example, display and voice generator); and notifies informationrequired for control to the control section 50.

The control section 50 makes a variety of predetermined controls withrespect to at least one of the transmitter section 21 and the receiversection 30 in accordance with a schedule (program) predetermined withrespect to this short range radar 20 or in response to a processingresult of the signal processor section 40.

Now, one example of operation of this short range radar 20 will bedescribed here.

The control section 50 sets a gain of the power amplifier 25 to apredetermined value in initial setting of an investigating operation bythis short range radar 20; sets a gain of the LNA32 at a maximum, forexample; and supplies a trigger signal G having a cycle Tg (for example,10 μs) to the pulse generator 23 of the transmitter section 21.

In this manner, when a pulse signal Pa having a width Tp (for example, 1ns) as shown in FIG. 11A is inputted to the oscillator 24 of thetransmitter section 21, the transmitter section 21 radiates a shortrange wave Pt having a width Tp to the space 1 at a carrier frequency Fc(for example, 26 GHz) as shown in FIG. 11B from the transmitter antenna22 via the power amplifier 25 and BRF 26.

At this time, power supply to the transmitter section 21 is provided toonly an output period of the short range wave Pt (or very limited periodincluding the output period) by means of the control section 50.

In this manner, a time interval at which power is supplied to thetransmitter section 21 is substantially 1/10000 of the whole cycle Tg,and thus, wasteful power consumption does not occur.

The short range wave Pt radiated from the transmitter section 21 isreflected by the object 1 a which exists in the space 1, and thereflection wave Pr is received by means of the receiver antenna 31 ofthe receiver section 30 after being delayed by a time interval Txcorresponding to a reciprocal distance from a transmission timing ofeach short range wave Pt to the object 1 a, as shown in FIG. 11C, forexample.

In the receiver section 30, after the signal R of the thus receivedreflection wave Pr has been amplified by means of the LNA32, theamplified signal is subjected to bandwidth limitation by means of theBPF 41, and noise power is reduced. In addition, after the signal R′ ofthe reflection wave Pr outputted from the BPF 41 has been branched intotwo sections, the first signal V1 and second signal V2 in phase by meansof the branch circuit 34 of the detector circuit 33, the branchedsignals are detected by means of the linear multiplier 35 and the lowpass filter 36, thereby detecting a baseband component W as shown inFIG. 11D.

On the other hand, in the sample hold circuit 37, a pulse signal Pchaving a width (for example, 1 ns) as shown in FIG. 11E is inputted tobe delayed by Td, 2Td, 3Td, . . . and nTd (n is an integer) from eachtransmission timing of the short range wave Pt.

Here, a description will be given with respect to a case in which thedelay time Td is equal to a width of the pulse Pc.

In addition, assuming that a distance up to a distal end of the space 1targeted for investigation is within 15 m, a time for a radio wave toreciprocate the distance of 15 m is substantially 100 ns.

Therefore, by delaying a transmission timing of a short range wave Pt bya maximum of 100 Td, as long as the reflection waves Pr is within therange of 15 m, these reflection waves Pr can be fully included incoverage.

As shown in FIGS. 11C, 11D, and 11E, the first to third pulse signals Pcdo not overlap a baseband component W, and thus, the sample hold circuit37 integrates only a noise component, and its integration result andhold value are substantially zero.

When fourth and fifth pulse signals Pc overlap a baseband component W,as shown in FIG. 11F, the baseband signal W is integrated within a highlevel period of the pulse signals Pc, and the integration results H1 andH2 are held. In this manner, the hold values H1 and H2 are convertedinto digital values by means of the A/D converter 39, and the converteddigital values are outputted to the signal processor section 40 in amanner as shown in FIG. 11G.

The signal processor section 40 detects a distance up to the object 1 aand the object size based on these hold values H1 and H2.

That is, when a hold value H equal to or greater than a predeterminedlevel has been inputted, for example, the signal processor section 40detects a distance up to the object 1 a according to how many samplingshave been performed before the input is obtained.

In addition, in the case where a hold value H equal to or greater than apredetermined level is continuous, the signal processor section 40detects the size of the object 1 a according to its continuous number.

This detection information is notified to the control section 50.

When the detection information notified from the signal processorsection 40 indicates that a distance up to the object 1 a is short, andthe intensity of the reflection wave Pr is high, the control section 50reduces a gain of the LNA2 of the receiver section 30 so that an inputlevel of the detector circuit 33 is within the range of linear operationof the linear multiplier 35.

In this case, the control section 50 controls a gain of the poweramplifier 25 of the transmitter section 21 to be reduced if necessary.

In this manner, during next investigation, a more precise basebandcomponent W is detected in the detector circuit 33 of the receiver 30.

In addition, in the case where the detection information notified fromthe signal processor section 40 indicates that there is a need foranalyzing a weak reflection wave Pr from the vicinity of a distal end ofan investigation space 1, the control section 50 controls a gain of thepower amplifier 25 of the transmitter section 21 to be increased.

In this manner, during next investigation, a more precise basebandcomponent W is detected in the detector circuit 33 of the receiversection 30.

In addition, the control section 50 makes control so as to obtainnecessary investigation information by appropriately varying theintegration time Tc of the sample hold circuit 37 according to the stateof the investigation space 1, the size of the object 1 a and the like.

In this case, although the control section 50 makes control for stoppingpower supply excluding only a period in which a short range wave Pt isradiated with respect to the transmitter section 21, this controlsection does not make such control with respect to the receiver section30 at all.

Hence, as described previously, in the case where a time intervalcorresponding to the investigation range is 100 ns, and the radiationcycle Tg of the short range wave Pt is 10 μs, in fact, only about 1/100in that cycle Tg is utilized.

Therefore, during the remaining period (that is, about 99/100 in thecycle Tg), power supply to the receiver section 30 is stopped by thecontrol section 50, and thereby power consumption can be furtherreduced.

In addition, for example, in the case where a hold output H equal to orgreater than a predetermined level cannot be obtained by radiation of100 short range waves Pt, the signal processor section 40 judges that noobject becomes an obstacle in the investigation range, and notifies thefact to the control section 50.

The control section 50 having received this notification stops powersupply to the transmitter section 21 and the receiver section 30 for apredetermined period (for example, 1 ms); restarts power supply afterelapse of the predetermined time; and makes control for repeating theinvestigating operation as described above.

Power consumption of the whole short range radars can be remarkablyreduced and battery can be driven by controlling power supply to thetransmitter section 21 and the receiver section 30 by means of thecontrol section 50.

In this manner, it becomes possible to provide portable short rangeradars.

In the foregoing description, in the sample hold circuit 37,investigation is made while a integration timing is shifted in a shortintegration time.

Hence, for example, at the initial stage of investigation, anintegration time is set at a time interval (for example, 100 ns)corresponding to an investigation distance (that is, is set to a fullrange), thereby making it possible to speedily grasp the presence orabsence of an object by one short pulse radiation.

Second Embodiment

FIG. 12 is a block diagram depicting a configuration of essentialportions of a second embodiment of short range radars according to thepresent invention.

As described above, in the integration type sample hold circuit 37according to the first embodiment, an electric discharge due to aleakage occurs, thus making it difficult to hold a voltage for a longperiod of time.

In such a case, as shown in FIG. 12, a plurality of sample holdcircuits, in this example, four sample hold circuits 37A, 37B, 37C, and37D and four A/D converters 39A, 39B, 39C, and 39D are provided inparallel.

In addition, for example, Pc (t), Pc (t+Te/4), Pc (t+Te/2), and Pc(t+3Te/4) may be applied from a pulse generator 38′ as a plurality ofpulse signals whose generation times are different from each other sothat the sample hold circuits 37A, 37B, 37C, and 37D each carry outintegration at their respectively different periods with respect to anoutput signal W of the detector circuit 33.

Namely, with respect to the above example of numeric values, the wholeintegration time Te is 100 ns, and the pulse generator 38′ provides fourpulse signals Pc (t), Pc (t+25 ns), Pc (t+50 ns), and Pc (t+75 ns) whosewidth is 25 ns (=Te/4) and each of which is delayed by 25 ns (=Te/4) toeach of the sample holds circuits 37A, 37B, 37C, and 37D.

Then, hold values Ha, Hb, Hc, and Hd from the sample hold circuits 37A,37B, 37C, and 37D may be outputted to the signal processor section 40after converted into digital values by means of the A/D converters 39A,39B, 39C, and 39D, respectively.

In this case, the signal processor section 40 analyzes whether or not anobject 1 a exists in an investigation space 1 based on at least one ofthe four hold values Ha, Hb, Hc, and Hd from the sample hold circuits37A, 37B, 37C, and 37D.

Even if the first three hold values Ha, Hb, and Hc cannot bediscriminated from among the four hold values Ha, Hb, Hc, and Hd due toelectric discharge caused by a leakage, during this analysis, the signalprocessor section 40 can analyze whether or not the object 1 a exists inthe investigating space 1 based on the immediately following fourth holdvalue Hd.

Third Embodiment

FIG. 13 is a block diagram depicting a configuration of essentialportions of a third embodiment of short range radars according to thepresent invention.

In FIG. 13, the same constituent elements having a configuration ofshort range radars according to the first embodiment shown in FIG. 1 aredesignated by the same reference numerals. A duplicate description isomitted here.

As described above, in the short range radars according to the presentinvention, a linear multiplier 35 is used for a detector circuit 33, andthereby there is no need for using a local signal unlike a conventionalquadrature type detector circuit for use in pulse radars. Thus, a shortpulse radar 20′ in a diversity system as shown in FIG. 13 can beprovided very easily.

In this short pulse radar 20′, two pairs of receiver sections 30A and30B and two pairs of A/D converters 39A and 39B allocated in a state inwhich respective receiving antennas 31 a and 31 b are spaced from eachother by a predetermined distance are provided with respect to onetransmitter section 21, one signal processor section 40, and one controlsection 50.

Then, with respect to signals of two reflection waves Pr and Pr′reflected in different directions from an object 1 a, the receiversections 30A and 30B each apply an detecting process using a linearmultiplier 35 and an integrating process using a sample hold circuit 37in the same manner as in the receiver section 30 according to the firstembodiment shown in FIG. 1. In addition, these two outputs Ha and Hb areconverted into digital signals by means of each of the A/D converters39A and 39B, and then, a delay time difference between the tworeflection waves Pr and Pr′ is detected by means of the signal processorsection 40, thereby making it possible to grasp a direction, a movingdirection and the like of the object 1 a.

Thus, even in the case where a plurality of receiver sections 30A, 30Aare provided, there is no need for local signal cable run or shieldinglike the receiver section 30 according to the first embodiment shown inFIG. 1. In addition, detection can be carried out by means of thedetector circuit 33 which includes independent linear multipliers 35,respectively, and thus, equipment designing of short range radarsbecomes very easy.

Therefore, as described above, according to the present invention, therecan be provided short range radars and control method thereof whichsolve the problems associated with the conventional technique, and whichis small in size and low in power consumption so as to be available inUWB.

1. A short range radar comprising: a transmitter section which radiatesa short range wave to a space; a receiver section having a detectorcircuit composed of a branch circuit which receives a reflection wave ofthe short range wave radiated to the space by means of the transmittersection and branches in phase a signal of the reflection wave into firstand second signals, a linear multiplier which linearly multiplies thefirst and second signals branched in phase by means of the branchcircuit, and a low pass filter which samples a baseband component froman output signal from the linear multiplier; a signal processor sectionwhich carries out an analyzing process of an object which exists in thespace based on an output from the receiver section; and a controlsection which makes a predetermined control with respect to at least oneof the transmitter section and the receiver section based on an analysisresult from the signal processor section.
 2. The short range radaraccording to claim 1, characterized in that the linear multiplier of thedetector circuit is composed of a Gilbert mixer.
 3. The short rangeradar according to claim 1, characterized in that the receiver sectionhas a sample hold circuit which carries out integration with respect toan output signal of the detector circuit and holds and outputs a resultof the integration.
 4. The short range radar according to claim 3,characterized in that the control section variably controls anintegration start timing and an integration time of the sample holdcircuit of the receiver section based on a processing result from thesignal processor section.
 5. The short range radar according to claim 3,characterized in that a plurality of sample hold circuits are providedas the sample hold circuit, and the plurality of sample hold circuitseach carry out integration in different periods from each other withrespect to the output signal from the detector circuit.
 6. The shortrange radar according to claim 1, characterized in that a poweramplifier which amplifies the short range wave is provided at thetransmitter section, a low noise amplifier which amplifies a signal ofthe reflection wave is provided at the receiver section, and the controlsection controls a gain of at least one of the power amplifier providedat the transmitter section and the low noise amplifier provided at thereceiver section so that a signal level of the reflection wave inputtedto the detector circuit of the receiver section is within a linearoperation range of the linear multiplier.
 7. The short range radaraccording to claim 1, characterized in that the transmitter section isprovided with: a pulse generator which generates a pulse signal having apredetermined width; and an oscillator which operates to oscillate onlyin a period in which the pulse signal from the pulse generator isinputted and outputs an output signal as the short range wave, and stopsthe oscillating operation in a period in which the pulse signal is notinputted.
 8. The short range radar according to claim 1, characterizedin that the control section stops power supply to the transmittersection in a period in which the transmitter section radiates the shortrange wave to the space, and radiates a next short range wave to thespace.
 9. The short range radar according to claim 1, characterized inthat the control section stops power supply to the receiver section in aperiod in which the transmitter section radiates the short range wave tothe space, and then, radiates a next short range wave to the spaceexcept a period in which a signal of a reflection wave relevant to theshort range wave radiated to the space is received by means of thereceiver section.
 10. The short range radar according to claim 1,characterized in that first and second receiver sections are provided asthe receiver section, each of which has first and second receivingantennas provided to be spaced from each other with a predetermineddistance in order to receive the reflection wave, and the signalprocessor section analyzes a direction of an object which exists in thespace based on output signals from the first and second receiversections.
 11. The short range radar according to claim 2, characterizedin that the Gilbert mixer used as the linear multiplier of the detectorcircuit comprises: a first differential amplifier comprising first andsecond transistors each having a base input end, a collector output end,and an emitter common current path, the emitter common current path ofthe first and second transistors being connected to a constant currentsource; a second differential amplifier comprising third and fourthtransistors each having a base input end, a collector output end, and anemitter common current path, the emitter common current path of thethird and fourth transistors being connected to a collector output endof the first transistor of the first differential amplifier; a thirddifferential amplifier comprising fifth and sixth transistors eachhaving a base input end, a collector output end, and an emitter commoncurrent path, the base input end of the fifth transistor being connectedin common to the base input end of the fourth transistor of the seconddifferential amplifier, the emitter common current path of the fifth andsixth transistors being connected to a collector output end of thesecond transistor of the first differential amplifier; a first loadresistor and a first output end connected in common to a collectoroutput end of the third transistor of the second differential amplifierand a collector output end of the fifth transistor of the thirddifferential amplifier, respectively; a second load resistor and asecond output end connected in common to a collector output end of thefourth transistor of the second differential amplifier and a collectoroutput end of the sixth transistor of the third differential amplifier,respectively; a first low pass filter including first and second coilsand a first resistor and a second low pass filter including third andfourth coils and a second resistor connected in series, respectively,between a first pair of lines and an earth line which transmits thefirst signal branched in phase by means of the branch circuit; a thirdlow pass filter including fifth and sixth coils and a third resistor anda fourth low pass filter including seventh and eighth coils and a fourthresistor connected in series, respectively, between a second pair oflines and an earth line which transmits the second signal branched inphase by means of the branch circuit; first and second emitter followercircuits comprising seventh and eighth transistors each having a baseinput end and an emitter output end, the base input ends of the seventhand eighth transistors each being connected to each of connectingneutral points of the first and second coils and the third and fourthcoils as each of the output ends of the first and second low passfilters; third and fourth emitter follower circuits comprising ninth andtenth transistors each having a base input end and an emitter outputend, the base input ends of the ninth and tenth transistors each beingconnected to each of connecting neutral points of the fifth and sixthcoils and the seventh and eighth coils as each of the output ends of thethird and fourth low pass filters; a fifth low pass filter composed of:a ninth coil connected between a common collector output end of thethird transistor of the second differential amplifier and the fifthtransistor of the third differential amplifier and the first loadresistor; a tenth coil connected between the common collector output endof the third transistor of the second differential amplifier and thefifth transistor of the third differential amplifier and the firstoutput end; and the first load resistor; and a sixth low pass filtercomposed of: an eleventh coil connected between a common collectoroutput end of the fourth transistor of the second differential amplifierand the sixth transistor of the third differential amplifier and thesecond load resistor; a twelfth coil connected between a commoncollector output end of the fourth transistor of the second differentialamplifier and the sixth transistor of the third differential amplifierand the second output end; and the second load resistor, wherein each ofthe base input ends of the first and second transistors of the firstdifferential amplifier is connected to each of the output ends of thefirst and second emitter follower circuits, respectively, and therebythe first signal branched in phase by means of the branch circuit isinputted to the first differential amplifier; and each of the base inputends of the third transistor of the second differential amplifier andthe sixth transistor of the third differential amplifier is connected toeach of the output ends of the third and fourth emitter followercircuits, respectively, and thereby the second signal branched in phaseby means of the branch circuit is inputted to the second and thirddifferential amplifiers, and thereby a linearly multiplied outputs ofthe first and second signals can be led out from at least one of thefirst and second output ends.
 12. A short range radar controlling methodcomprising the steps of: preparing a transmitter section, a receiversection, and a linear multiplier; radiating a short range wave to aspace by means of the transmitter section; receiving a reflection waveof the short range wave radiated to the space by means of the receiversection to branch in phase a signal of the reflection wave into firstand second signals; linearly multiplying the first and second signals bymeans of the linear multiplier to output a linearly multiplied signal;sampling a baseband component from an output signal of the linearmultiplier; carrying out an analyzing process of an object which existsin the space based on the baseband component; and making a predeterminedcontrol with respect to at least one of the transmitter section and thereceiver section based on a result of the analyzing process.
 13. Theshort range radar controlling method according to claim 12,characterized in that the step of outputting the linearly multipliedsignal comprises the step of carrying out linear multiplication foroutputting the linearly multiplied signal by using a Gilbert mixer asthe linear multiplier.
 14. The short range radar controlling methodaccording to claim 12, characterized by further comprising the step of,before the step of carrying out the analyzing process, carrying outintegration with respect to the baseband component and holding andoutputting a result of the integration.
 15. The short range radarcontrolling method according to claim 14, characterized in that the stepof carrying out integration with respect to the baseband componentcomprises the step of variably controlling a start timing of integrationand an integration time with respect to the baseband component based onthe result of the analyzing process.
 16. The short range radarcontrolling method according to claim 14, characterized in that the stepof carrying out integration with respect to the baseband componentcomprises the step of carrying out integration in a plurality of periodsdifferent from each other with respect to the baseband component byusing a plurality of sample hold circuits.
 17. The short range radarcontrolling method according to claim 12, characterized in that a poweramplifier which amplifies the short range wave is provided at thetransmitter section, a low noise amplifier which amplifies a signal ofthe reflection wave is provided at the receiver section, and the step ofmaking the predetermined control comprises a step of controlling a gainof at least one of the power amplifier provided at the transmittersection and the low noise amplifier provided at the receiver section sothat a signal level of the reflection wave at the receiver section iswithin a linear operation range of the linear multiplier.
 18. The shortrange radar controlling method according to claim 12, characterized inthat the step of radiating a short range wave to a space by means of thetransmitter section comprises the steps of: generating a pulse signalhaving a predetermined width; making an oscillation operation only in aperiod in which the pulse signal is inputted to output an output signalas the short range wave; and stopping an oscillation operation during aperiod in which the pulse signal is not inputted so as not to output anoutput signal as the short range wave.
 19. The short pulse radarcontrolling method according to claim 12, characterized in that the stepof making the predetermined control comprises the step of: stoppingpower supply to the transmitter section in a period in which thetransmitter section radiates the short range wave to the space, andthen, radiates a next short range wave to the space.
 20. The short rangeradar controlling method according to claim 12, characterized in thatthe step of making the predetermined control comprises the step of;stopping power supply to the receiver section in a period in which thetransmitter section radiates the short range wave to the space, andthen, radiates a next short range wave to the space except a period inwhich a signal of a reflection wave with respect to the short range waveradiated to the space is received by means of the receiver section. 21.The short range radar controlling method according to claim 12,characterized in that first and second receiver sections are provided asthe receiver section, each of which has first and second receivingantennas provided to be spaced from each other with a predetermineddistance in order to receive the reflection wave, and the step ofcarrying out the analyzing process comprises the step of analyzing adirection of an object which exists in the space based on output signalsfrom the first and second receiver sections.
 22. The short range radarcontrolling method according to claim 12, characterized in that, in thestep of outputting the linearly multiplied signal, the Gilbert mixerused as the linear multiplier comprises: a first differential amplifiercomprising first and second transistors each having a base input end, acollector output end, and an emitter common current path, the emittercommon current path of the first and second transistors being connectedto a constant current source; a second differential amplifier comprisingthird and fourth transistors each having a base input end, a collectoroutput end, and an emitter common current path, the emitter commoncurrent path of the third and fourth transistors being connected to acollector output end of the first transistor of the first differentialamplifier; a third differential amplifier comprising fifth and sixthtransistors each having a base input end, a collector output end, and anemitter common current path, the base input end of the fifth transistorbeing connected in common to the base input end of the fourth transistorof the second differential amplifier, the emitter common current path ofthe fifth and sixth transistors being connected to a collector outputend of the second transistor of the first differential amplifier; afirst load resistor and a first output end connected in common to acollector output end of the third transistor of the second differentialamplifier and a collector output end of the fifth transistor of thethird differential amplifier, respectively; a second load resistor and asecond output end connected in common to a collector output end of thefourth transistor of the second differential amplifier and a collectoroutput end of the sixth transistor of the third differential amplifier,respectively; a first low pass filter including first and second coilsand a first resistor and a second low pass filter including third andfourth coils and a second resistor connected in series, respectively,between a first pair of lines and an earth line which transmits thefirst signal branched in phase by means of the branch circuit; a thirdlow pass filter including fifth and sixth coils and a third resistor anda fourth low pass filter including seventh and eighth coils and a fourthresistor connected in series, respectively, between a second pair oflines and an earth line which transmits the second signal branched inphase by means of the branch circuit; first and second emitter followercircuits comprising seventh and eighth transistors each having a baseinput end and an emitter output end, the base input ends of the seventhand eighth transistors each being connected to each of connectingneutral points of the first and second coils and the third and fourthcoils as each of the output ends of the first and second low passfilters; third and fourth emitter follower circuits comprising ninth andtenth transistors each having a base input end and an emitter outputend, the base input ends of the ninth and tenth transistors each beingconnected to each of connecting neutral points of the fifth and sixthcoils and the seventh and eighth coils as each of the output ends of thethird and fourth low pass filters; a fifth low pass filter composed of:a ninth coil connected between a common collector output end of thethird transistor of the second differential amplifier and the fifthtransistor of the third differential amplifier and the first loadresistor; a tenth coil connected between the common collector output endof the third transistor of the second differential amplifier and thefifth transistor of the third differential amplifier and the firstoutput end; and the first load resistor; and a sixth low pass filtercomposed of: an eleventh coil connected between a common collectoroutput end of the fourth transistor of the second differential amplifierand the sixth transistor of the third differential amplifier and thesecond load resistor; a twelfth coil connected between the commoncollector output end of the fourth transistor of the second differentialamplifier and the sixth transistor of the third differential amplifierand the second output end; and the second load resistor, wherein each ofthe base input ends of the first and second transistors of the firstdifferential amplifier is connected to each of the output ends of thefirst and second emitter follower circuits, respectively, and therebythe first signal branched in phase by means of the branch circuit isinputted to the first differential amplifier, each of the base inputends of the third transistor of the second differential amplifier andthe sixth transistor of the third differential amplifier is connected toeach of the output ends of the third and fourth emitter followercircuits, respectively, and thereby the second signal branched in phaseby means of the branch circuit is inputted to the second and thirddifferential amplifiers, and thereby a linearly multiplied outputs ofthe first and second signals can be led out from at least one of thefirst and second output ends.